In order to prevent oxygen oxidation and store various types of articles, represented by foods, beverages, medicinal products, cosmetics, etc., which easily deteriorate or degrade under the effect of oxygen for a long time, oxygen absorbents are used for removing oxygen within packaging bodies storing these articles.
As the oxygen absorbent, an oxygen absorbent containing an iron powder as a reactive main component is generally used in view of oxygen-absorbing ability, handling and safety. However, the iron-based oxygen absorbent is responsive to a metal detector and thus it is difficult to use a metal detector in inspecting foreign matter. Furthermore, packaging bodies containing an iron-based oxygen absorbent have a risk of ignition, and thus, they cannot be heated by a microwave oven. Moreover, the oxidation reaction of an iron powder requires water, and thus, an oxygen-absorbing effect is exerted only when the article to be packed is rich in moisture content.
Packaging containers are developed by making the container of a multilayer material having an oxygen-absorbing layer formed of an oxygen-absorbing resin composition containing a thermoplastic resin and an iron-based oxygen absorbent, thereby improving a gas barrier property of the container and providing an oxygen-absorbing function to the container itself (see, Patent Document 1). However, such a multilayer container has the same problems: a metal detector cannot be used; heating cannot be made by a microwave oven; and the effect is only exerted on an article to be packed rich in moisture content. In addition, the multilayer container has a problem of opacity, leading to insufficient visibility of content.
In the aforementioned circumstances, it has been desired to develop an oxygen absorbent containing an organic substance as a reactive main component in place of an iron-based oxygen absorbent. As the oxygen absorbent containing an organic substance as a reactive main component, for example, an oxygen absorbent containing ascorbic acid as a main component is known so far (see, Patent Document 2).
In the meantime, an oxygen-absorbing resin composition composed of a resin and a transition metal catalyst is known. For example, a resin composition composed of a polyamide as an oxidizable organic component (in particular, a xylylene group-containing polyamide) and a transition metal catalyst, is known (see, Patent Document 3). In Patent Documents 3, articles obtained by molding a resin composition, such as an oxygen absorbent, a packaging material and a multilayer laminated film for packaging are also exemplified.
As an oxygen-absorbing resin composition requiring no moisture content for absorbing oxygen, an oxygen-absorbing resin composition composed of a resin having a carbon-carbon unsaturated bond and a transition metal catalyst, is known (see, Patent Document 4).
As a composition for trapping oxygen, a composition composed of a polymer containing a substituted cyclohexene ring or a low molecular-weight substance bound with the cyclohexene ring and a transition metal is known (see, Patent Document 5).